The present disclosure relates, in various exemplary embodiments, to layered photoresponsive devices, imaging apparatuses and processes thereof. More specifically, the exemplary embodiments relate to improved layered photoresponsive devices comprised generally of a charge transport layer and a photogenerating layer. The photogenerating layer contains porphine or its derivatives to reduce ghosting or other related print defects.
The layered photoresponsive devices of the exemplary embodiments are useful as imaging members in various electrostatographic imaging systems, including those systems wherein electrostatic latent images are formed on the imaging member. For example, imaging members can be used in electrophotographic, electrostatographic, xerographic and like devices, including printers, copiers, scanners, facsimiles, and including digital, image-on-image, and like devices. More particularly, the embodiments pertain to a photoreceptor that incorporates specific molecules to facilitate charge generation while suppressing ghosting and improving photoreceptor performance.
Electrophotographic imaging members, e.g., photoreceptors, typically include a photoconductive layer formed on an electrically conductive substrate. The photoconductive layer is an insulator in the substantial absence of light so that electric charges are retained on its surface. Upon exposure to light, charge is generated by the photoactive pigment, and under applied field charge moves through the photoreceptor and the charge is dissipated.
In electrophotography, also known as xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light. Charge generated by the photoactive pigment move under the force of the applied field. The movement of the charge through the photoreceptor selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image. This electrostatic latent image may then be developed to form a visible image by depositing oppositely charged particles (such as toner particles) on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The imaging process may be repeated many times with reusable imaging members.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material such as vitreous selenium or it may be a composite layer containing a photoconductor and another material. In addition, the imaging member may be layered. These layers can be in any order, and sometimes can be combined in a single or mixed layer.
Typical multilayered photoreceptors have at least two layers, and may include a substrate, a conductive layer, an optional charge blocking layer, an optional adhesive layer, a photogenerating layer (sometimes referred to as a “charge generation layer,” “charge generating layer,” or “charge generator layer”), a charge transport layer, an optional overcoating layer and, in some belt embodiments, an anticurl backing layer. In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). Enhancement of charge transport across these layers provides better photoreceptor performance.
“Ghosting” is a typical printing defect. Ghosting is thought to result from the accumulation of charge somewhere in the photoreceptor. Consequently, when a sequential image is printed, the accumulated charge results in image density changes in the current printed image that reveals the previously printed image.
Ghosting patterns form either lighter images than the background or darker images than the background. In instances where the ghost image is lighter than the background, this phenomena is known as “negative ghosting” and where the ghost image is darker than the background, this phenomenon is known as “positive ghosting.” Because the ghosting phenomenon is complex and results from actual electrostatic printer or copy machine system characteristics, toner flowability, toner triboelectric charge properties, and even exponential memory decay time of the photoconductor, the underlying cause is still not entirely understood.
Ghosting can occur in a photoreceptor when a residual image remains in the photoreceptor, and specifically within the charge generating layer. Ghosting, in certain instances and if attributable to the photoreceptor or imaging member, can be remedied by ensuring more thorough erasure, such as by greater exposure to light of a suitable wavelength. Although satisfactory in certain applications, a need remains for another strategy to reduce the potential for ghosting in a photoreceptor or other like imaging member.